Digital reader



June,9, 1953 G. w. KING 2,541,522

DIGITAL READER Filed Jan. 14, 1950 4 Sheet' s-Sheet l INVENTOR. GILBERT w. KING H/5 ATTORNEYS.

G. W. KING DIGITAL READER June 9, 1953 4 Sheets-Sheet 2 Filed Jan. 14, 1950 wk. N: V: 2

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G. w. KING DIGITAL READER June 9, 1953 4 Sheets-Sheet 5 Filed Jan. 14, 1950 BIN H V m BNM INVENTOR.

GILBERT W- KING w E N m T T A 6 H June 9, 1953 G. w. KING 2,641,522

DIGITAL READER Filed Jan. 14, 1950 4 Sheets-Sheet 4 k 25 5 m I 8 2 g 0 2 0 Y O U 2 L N a INVENTOR.

-G|LBERT W. KING HIS ATTORNEYS.

Patented June 9, 1953 DIGITAL READER Gilbert W. King, South Lincoln, Mass, assignor to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Application January 14, 1950, Serial No. 138,652

17 Claims.

1 The present invention relates to devices'for indicating or recording instantaneous values of a variable. More particularly, it has to do'with new and improved apparatus for converting instantaneous values of a variable to digital num- "bers which may be recorded in any suitable manner as in the form of perforations on cards, for example.

In the present practice, experimental data are usually recorded either by hand or by automatic recording devices such as the pen-galvanometer,

for example. Generally the manual method is employed only when the data to be recorded are few in number and the time between successive readings is long enough to permit observation by the human eye and recording by hand. Where 'a large sample is desired for'statistical treatment, .or where the readings are required to be taken at a rate faster than the human eye .and hand can respond, the automatic recording method is used.

'In certain cases, however, as where the readings are discontinuous or subject to large fluctuations,

automatic recording apparatus of the type available heretofore cannot be used since it does not respond quickly enough to give the desired accuracy at high speeds of operation. Further, if

a large number of sets of graphical data are recorded inthe form of curves, for example, and

have to be calibrated or corrected, and compared :with each other, for example, treatment of the data becomes cumbersome and time consuming,

evenwhe'n the data are recorded automatically by a pen-galvanometer, for example, since this involves manually reading off points from the recorded curve'or' curves, applying some calcula tion to the readings and sometimes replotting the corrected readings.

It is an object of the invention, accordingly; to provide new and improved apparatus for converting instantaneous values, or average values 'value of a continuous physical variable such as a voltage, averaged over a time interval of adjustable length, into a digital number.

Another object of the invention is to provide new and improved variable to digital conversion apparatus of the above character which is simple in construction and which embodies a minimum number of components.

Yet another object of the invention is to provide new and improved digital conversion apparatus of the above character which is adapted to convert instantaneous values of a variable quantity, averaged over a given time interval, to binary digital numbers. I

A still further object of the invention is to provide new and improved digital conversion apparatus of the above character which is adapted to convert instantaneous or average values ofa variable to a digital number without loss of accuracy, namely, by using a unit in the binary system of representation whose value is equal to or slightly less than the noise level inherently and universally present in the variable being measured, said choice being in accordance with the best practice described by the present day theory of communication.

A further object of the invention is to provide new and improved digital conversion apparatus of the above character in which digital numbers representing instantaneous or average values of a variable may be indicated visually or recorded.

These and other objects of the invention are attained by impressing a voltage representing an instantaneous or average value of a variable, successively, on a plurality of relay devices which are biased at values corresponding to successive binary digits, respectively. A sufiicient number of relay devices are employed to reproduce, to the required degree of accuracy, the highest digital number that is to be recorded.

With each relay device is associated electrical switching means which functions automatically 'to transfer the input signal applied to a preceding relay-device to the next succeeding relay device.

the input signal to a preceding relay device is sufficiently large to render that device operative,

the switching means operates automatically to supply to the next succeeding relay device the difference between the signal input to the preceding relay device and the bias applied thereto.

Each relay device rendered operative as described above may cause a corresponding visual indicator to be operated or a suitable record to be made such as a perforation in a card, for example. V

Where the signal to be converted is changing at 'a relatively rapid rate, means is provided for sampling the instantaneous values of the signal at the beginning of each conversion cycle, the sample values thus obtained being converted to digital numbers as described above.

With the construction described above, instantaneous values of a variable may be readily converted to digital binary numbers. Further, the novel switching means embodied in the apparatus functions to prevent operation of a relay device unless it should actually be operated, thus avoiding inadvertent errors.

The invention may be better understood from the following detailed description of several representative embodiments thereof, taken in conjunction with the accompanying drawings in which:

Fig. l is a schematic diagram of a basic component of digital conversion apparatus constructed according to the invention;

Fig. 2 illustrates schematically a preferred form of basic component according to the invention;

Fig. 3 is a schematic diagram showing a typical sampling means and timing mechanism for digital conversion apparatus constructed according to the invention;

Fig. 4 shows schematically a plurality of. relay devices in a typical digital conversion system, together with the switching means therefor;

Fig. 5 illustrates schematically representative indicating and recording means for a digital conversion system; and

Fig. 6 is a schematic diagram of a typical combined relay and Microswitch that may be employed in the digital conversion apparatus.

In the several typical forms of the invention to be described below, it is assumed that the variable to be recorded can be represented by a voltage of corresponding magnitude. As a practical matter, almost all physical variables of which experimental measurements are desired can be so represented. A typical example the measurement of light intensity by a photomultiplier tube which, on exposure to the light, develops a corresponding voltage across a load resistor.

According to the invention, the voltage representing the variable is compared successively'with each one of a plurality of voltages corresponding in magnitude with successive digital positions in a binary number system, respectively. The largest of the latter voltages, and the one against which the voltage corresponding to the variable to be measured is compared first, has a magnitude representing the highest power. of two that could I occur, 1. e., the upper limit of the voltage to be recorded. The magnitudes of the succeeding voltages against which the voltage representing the variable is compared represent successively lower powers of two,. there being as many as may be required to measure the voltage to be recorded to the desired degree of accuracy;

If at any comparison stage the voltage representing the variable to be measured happens to be larger than the, comparison voltage, only the difference between the two voltages is passed on for comparison with the voltage representing the next lower power oftwo. At the same time, means may be initiated for producing an indication or a record. On the other hand, if the voltage representing the variable is smaller than the comparison voltage, the former voltage is passed on unchanged for comparison with the voltage representing the next lower power of two.

The voltages used. for comparison and for subtraction from the input signal, when required, can be obtained from any convenient reliable source. In the circuits described here batteries are used as an example. Storage batteries when well charged, or dry cells are generally satisfactory. It is well known that the so-called Standard Cell, such as a calomel cell, supplies a comparison voltage of a high degree of stability and of a value known to several significant figures. These cells are preferred means of measuring voltages in physical and physical-chemical experiments.

Thus, in recording measurements of a precise physical or physical-chemical experiment, very accurately known, accepted, and preferred standard voltages are available for the fundamental comparison and subtraction circuits of this invention'. Those circuits then constitute preferred apparatus for reading voltages. However, it is possible to incorporate an electronic source of comparison and subtraction voltage when the use of batteries or standard cells is inconvenient.

A typical circuit element having the mode of operation described above is shown in Fig. 1. It comprises an electron tube ID, having a grid ll connected to the negative terminal of a source of bi'asing voltage l2, the positive terminal of which is connected to an input lead 13. The lead. ['3 may be provided with a shield 49 which is grounded as shown. The" grid H is also connected by a conductor 14 to one contact l5 of a relay I6, the winding of which is' interposed between a suitable source of plate supply B+ and the plate I! of the tube In.

The input lead I3 is also connected by a con.- ductor I 8 to another contact IS on the relay l6. Normally, the contact I9 is engaged by a contact arm 20 which is connected by a conductor 2! to anoutput terminal 22. Uponenergization of the relay 18, the contact arm 20 disengages the contact l9 and engages the contact [5.

In operation, let it. be assumed that the bias voltage provided by the source l2 corresponds to the value of a selected power of two. If now. the voltage at the input lead l3 representing the variable: to be measured is positive and is larger than the biasvoltage, the tube It! will become conducting, energizing "the relay l8 and causing themovable contact arm 28* to disengage the contact I19 and to enga'gethe contact IS. The output passed on to the next stage at the terminal 22 is, therefore, the difference between the voltage to be measured and the bias voltage. If, however, the input voltage at the input lead 13 is less than thebias voltage, the tube l0 remains nonoonducting and the movable contact arm 20 remains in engagement with the contact [9. The output to the, next stage, in, this case, is the input at the lead 13, without change.

Because of. uncertainties in the performance of the average relay, such aschattering and wide differencesin the opening" and closing times of supposedly identical relays, for example, it is de sirable touse two relays to switch either the input to a stage or the input to the control grid of the tube in. that stage to the next succeeding stage, as: is shown in Fig. 2.

In Fig. 2, the signal input which may be received from a photocell device I311, for example, at the input terminal 13 is supplied through a source of negative biasing voltage 23 and a resistor 24 to the control grid 25 of. a conventional four electrode gas discharge device 26. The cathode 2'! and the screen grid 28 ofthe device 25 may be connected to ground at 29 and a condenser 3B preferably connected between the grid 25 and they cathode 21 in order to prevent possible firing of the tube 26 from spurious signal pickup.

The. plate 3| of the gas discharge device 26 is connected by' a conductor 32 in series with the winding of a relay 33 having a movable contact 3 adapted to engage selectively either of two flxed contacts and 33. The movable contact 34 is connected by a conductor 31 to an output terminal 38, while the fixed contact 36 is connected by a conductor 39 to the movable contact of a relay 4| which, in an actual digital conversion system, may be energized by suitable timing mechanism, as will be described in greater detail below. The fixed contact 35 on the relay 33 is connected by a conductor 42 to a fixed contact 43 on the relay 4| which is also connected by a conductor 44 to the negative terminal of the source of bias voltage 23. A second contact on the relay 4| is connected by a conductor 46 to the positive terminal of the source of biasing voltage 23 and to the input lead I3.

Normally, the gas discharge device 26 is maintained nonconducting by the negative bias impressed upon the control grid 25 by the source 23. The voltage input I3 which is to be measured,

is impressed upon the control grid 25 in series with the source of bias voltage 23. If the bias voltage is greater than the voltage to be measured, the gas discharge device 26 remains nonconducting so that when the relay 4| is subsequently energized by the timing mechanism, the voltage to be measured is passed on to the next succeeding stage through a circuit which is traced from the input lead I3 through the conductor 46, the relay contact 45 engaging contact arm 40, the

conductor 39, the relay contact 36 engaging the contact arm 34 and the conductor 31 to the output terminal 38.

If, however, the voltage to be measured is larger than the bias voltage, the gas discharge device 26 becomes conducting and the relay 33 is energized. This causes the contact arm 34 to disengage the contact 36 and to engage the contact 35. Under these conditions, the difference between the voltage to be measured and the bias voltage is passed on to the next stage through a circuit which is traced from the input lead I3 through the conductor 46, the source of bias voltage 23, the conductors 44 and 42, the fixed contact 35 engaging movable contact arm 34, and the conductor 31 to the output terminal 38. The subsequent energization of the relay 4| by the timing mechanism does not affect this circuit in any way.

A representative digital conversion system comprising a plurality of elements of the type shown in Fig. 2 is illustrated in Figs. 3, 4, 5 and 6. Since in some cases the voltage to be read may vary at an extremely rapid rate, it is desirable to provide sampling circuit means for measuring instantaneous values of the voltage to be measured at times just prior to the initiation of the successive conversion cycles. A typical sampling circuit 4! (Fig. 3) may comprise a conventional electron tube I40 having a control grid I4| connected to the input lead I3, and having a cathode I42 connected through a resistor I43 to ground at 4B, the shield 49 for the input lead I3 also being grounded through a conductor 50.

The tube I40 is preferably connected as a cathode follower and its plate 5| is connected by a conductor 52 to the positive terminal of a suitable source of plate supply voltage (not shown). The output from the tube I43 is fed from its cathode I 42 by a conductor 53 to a fixed contact 54 on a relay 56 which is adapted to be engaged by a movable contact arm 55.

Connected between the relay movable contact arm 55 and ground is a fixed condenser 51 which is adapted to be charged by the output of the cathode I42 of the cathode follower I40 to a value proportional to the voltage to be measured, when the relay 56 is energized to bring its movable contact into engagement with the contact 54. The voltage thus impressed on the condenser 51 is fed through a conductor 58 to the control grid 59 of a second electron tube 60, which may be mounted in the same envelope as the tube I40, if desired, and which is also preferably connected as a cathode follower. Thus, the plate 6| of the tube 60 is connected by the conductors 62 and 52 to the positive terminal of the source of plate supply voltage, and the cathode 63 is connected through a cathode resistor 64 to ground. At the end of each conversion cycle, the condenser 5! is adapted to be discharged to ground through a circuit including a resistor '65, a conductor 66, the contacts 8|f and 92 of the timing relay 12 and a conductor I54 as will be described later in greater detail.

The sampling relay E6 is adapted to be energized once at the beginning of each conversion cycle through a circuit which is traced from the positive terminal of the plate voltage supply through the conductors 52 and I8, a movable contact arm 71 on a Microswitch I44 which normally engages a fixed contact H5, a conductor I I8, a fixed contact I2'I engaged by a movable contact arm I29 on a relay I20, a conductor I30, the relay 56 and a resistor I45 to ground.

The Microswitch I44 is adapted to be actuated upon energiaation of the punching relay I6 (Figs. 3 and 6) at the end of a conversion cycle, and the circuit traced out above is completed when the Microswitch contact arm 11 subsequently returns to its normal position in engagement with the contact I I5. Upon energization of the relay 56, the movable contact arm 55 engages the contact 54, permitting the sampling condenser 51 to charge up to the voltage output at the cathode I42 of the tube I40.

At the instant that the Microswitch movable contact arm 11 returns to its normal position in engagement with the contact I|5, electrical energy is also impressed upon a parallel circuit having, in one branch, the series connected relays II9 and I20 and a condenser I22 in another branch. Thus, one end of the parallel circuit is connected to the conductor IIS and the other is connected through a resistor I2I to ground. While the relay I 20 is deenergized, the sampling relay 56 remains energized through the circuit traced above. Energization of the relay I20 deenergizes the relay 56 and disconnects the sampling condenser 51 from the cathode I42 of the tube I40. Energization of the relay |I9 causes its movable contact I25 to engage a fixed contact I23, thereby connecting the positive terminal of the plate supply voltage through the conductors 52, I24 to a conductor I4, thereby initiating operation of timing mechanism to be described later.

The purpose of the condenser I22 is to delay energization of the relays II9 and I 20 until the sampling condenser has had time to charge to the voltage at the cathode I42 of the tube I40. After the condenser 57 is fully charged, it is disconnected from the cathode I42 by operation of the relays I20 and 56, and its voltage remains sensibly constant throughout the conversion cycle.

The output of the cathode follower tube 60 is continuously applied through a conductor 61 to the first of a plurality of digital conversion stages 63a, 68b, 68c, 68d, 58e, 53f and 689' (Fig. 4). In order to counteract the steady current from the cathode follower tube 60, it is desirable to include a suitable source of voltage 69 in series with the conductor .61, as shown. In any speciflcdigital conversion system, the number of counter stages employed will depend upon the degree of accuracy desired. In 4, a system employing only seven stages is shown, for example, as required to give an accuracy of reading of 1%.

Except for the last stage 680, the several counter stages are identical with the single stage shown in Fig. 2, and corresponding parts in the former have been designated by corresponding reference characters with appropriate lett The last stage 38g differs from Fig. 2 in that relays corresponding to the relays 4I and 43 have been eliminated because they are not needed. Further, the movable contact 34; of the relay 33% is connected to ground through a resistor 19,

which is by-passed by a conductor 11. This prevents any rise in grid potentials while the movable contact arms on the relays are between contacts and results in improved stability,

The relays @Ia, Mb, lic, 4Id, 4Ie dIf are adapted to be energized successively by suitable timing mechanism which may comprise, for example, a plurality of timing relays 12a, 12b, 12c, 12d, 12c and 121 (Fig. 3). One terminal of the relay 12a is connected by the conductors 13a and 14 to the fixed contact 15 on the Microswitoh I44, which is adapted to be engaged by the movable contact 11, the latter being connected through the conductors 18 and 52 to the positive terminal of the source of plate supply voltage. As best shown in Fig. 6, the Microswitch I 54 is adapted. to be actuated by the punching relay 13 when the latter is eiergized. The relay 12a is also connected by a conductor 19a through the winding of the relay 4-Ia (Fig. 4) and a resistor 32a to ground (Fig. 3).

The relay 120. has a fixed contact 8 Ia connected by a conductor I4-Ii-a to the conductor 14. The contact 81a is adapted to be engaged by a movable contact 82c, which is connected by a conductor 13b to one terminal of the next succeeding relay 12b. The other terminal of the relay 12b is connected in series with the relay 4Ib (Fig. 4) and a resistor 88?: to ground (Fig. .3). In similar fashion, each of the remaining relays 12c, 12d, 12c and 12; are adapted to be connected to the positive terminal of the source of plate supply through contacts on the preceding relay, and are connected to ground through the corresponding relays 4Ic, Md, 4Ie and 4I in the several counter stages (Fig. f1) and the resistors 80c, 80d, 80c and 86 in the timing mechanism (Fig. 3),

Connected in the plate circuits of the respective gas discharge devices 26a, 26b, c, 25d, 25e, 26] and (Fig. 4) are a plurality of relays 83a,

83b, 83c, 83d, 83e, 83f and 83g, respectively (Fig.

5). The relays 83b, 83c, 83d, 83e, MI and 839 are identical in construction and it Willbe necessary to describe only one in detail, corresponding parts in the others being designated by corresponding reference characters with appropriate letters. Relay 831) has a movable contact arm 84b which normally engages a fixed contact 852), and which is adapted to engage a second contact I5Ib. The movable contact arm 84b is connected to a conductor BI and the contact Iiilb is connected by a conductor 8% to a terminal IOUb on a suitable recording device IOI which may be conventional IBM card perforating punch, for example, such as shown in the United States patent to Palmer et al., No. 2,536,955, dated January 2, 1951.

Associated with the relay 83b is an indicating circuit comprising, for example, a neon tube 96b and a series resistor 9113. This indicating circuit is adapted to be energized by a circuit which is traced from the positive terminal of the source of plate supply through the conductors and 88, the resistor 91b, the tube 9617, the conductor 9i, a movable contact 92 of a switch 93, adapted to engage a fixed contact 94, and ground 95. The relay contact 85?) is connected to the junction between the resistor 91b and the tube 9617. Since the movable contact arm 84b normally engages the contact 851), the neon light 96b is short-circuited so that it is not lighted. When the relay 53b is energized, however} the movable contact arm 84b disengages the contact 851), breaking the shunt circuit so that if the contact arm 92 of the sv itch 93 is moved into engagement with the fixed cont-act 84 the neon lamp 962) will be lighted.

The relay 83!! serves as a control to indicate that the voltage to be read has gone oil scale." i, c. has risen above a predetermined value determined by the source 23a. To this end, the conductor BI is connected to the fixed relay contact 85a which is normally engaged by the contact arm 84a, and the latter is connected through the conductors 86a and Hi, the normally open contacts H3 and H4 on the relay 16 (Fig. 3) and a conductor II1 to the contact I02 on the punch IIlI (Fig. 5).

It will be understood, therefore, that if the relay 83a is not energized during a conversion cycle, but one or more of the relays 83b, 83c, 83d, 33c, 3] and 839 are energized, the closing of the contacts IIB and H4 upon energization of the relay IS will complete connections between the punch terminal I62 and any of the terminals IBOb, III-3c, mild, I350, I00) and N10, for which a corresponding relay 83b, 83c, 83d, 83e, 83f and 839 has been energized, thereby operating the punch iiii and causing it to punch holes corresponding to the binary number to be recorded, in a card. If the relay 83a has been energized, however, the opening of the contacts 84a and 85:! makes it impossible for the punch terminal I122 to be connected to any of the terminals IOIib, IUOc, Iflfld, IDDe, Iilllf and I009, and the punch IIJI, therefore, is rendered inoperative. If desired, the contact I5I a may be connected by a conductor a to a punch terminal IIJGa which will cause the punch IOI to record an X, for example, when the relay 16 is energized.

An indicating circuit comprising a resistor 91a and a neon tube 96a may be connected across the conductors SI and 86a, and the latter conductor may be connected to the conductor 89 by a resistor 810. which prevents interference with the punch circuits when the relay 83a is not energized. Normally, the tube 96a is short-circuited by the engaged contacts 84:: and 85a of the relay 83a. Energization of the latter opens its contacts, causing the tube 95a to be lighted and indicating that the voltage to be read has gone off scale.

Operation of the punch IIJI (Fig. 5) at the conclusion of each conversion cycle may be effected by means of a relay I 03 (Fig. 3) connected in series with the timing relay 12d. The relay I03 has a movable contact arm I04, normally engaging a fixed contact I05, which is adapted to be moved into engagement with a fixed contact I06. Connected between the movable contact arm I04 and ground I01 is a condenser 458. When the movable contact arm I04 is in engagement with the contact I05, as shown in Fig, 3, the condenser I88 is adapted to be charged through a resistor I09 and a conductor IIO connected to the positive terminal of the source of plate supply.

Upon energization of the relay I 03, the movable contact arm I04 disengages the contact I05 and engages the contact I06, thereby impressing the voltage across the condenser I08 on the relay 16 through the conductors III and H2. The relay I6 is not fully energized until a predetermined time has elapsed as determined by the value of the condenser- I08 and the amount of inductance in the relay I6, if any. Preferably, the system is designed so that full energization of the relay I6 takes place shortly after the timing relay 12) has been energized. Further, the condenser I08 is of such a size that the time constant of the circuit including it and the coils of the relay I6 keeps the latter closed long enough to actuate the punch IOI.

Energization of the relay I6 also actuates the Microswitch I44 (Figs. 3 and 6) causing its contact arm to become disengaged from the contact I I5 and to engage the contact I5, as stated above.

Operation Initially, the biasing voltages provided by the sources 23a, 23b, 23c, 2311, 23e, 23f and 239 are selected to be proportional to successive powers of two, that provided by the last source 239 being approximately equal to the noise level in the system and that provided by the source 23a being proportional to the largest power of two needed to convert the maximum expected value of the voltage to be measured to a digital number. Thus, in a typical circuit, the-bias voltages supplied by the sources 23a, 23b, 23c, 2311, 23e, 23f and 23g might be 100, 50, 25, 12.5, 6.2, 3.1 and 1.5 Volts, respectively.

In operation, the voltage to be read, namely, the input at the conductor I3 (Fig. 3) which is a function of the intensity of light falling on the photocell I3a, is continuously applied to the grid I4I of the tube I40, so that the voltage at the cathode I42 varies in a corresponding manner. Assuming that the filaments of the tubes are warmed up and that plate supply voltage is being fed to the system, the relay 56 is energized through a circuit which is traced from the positive terminal of the source of plate supply voltage through the conductors 52 and I8, the movable contact arm 11 on the Microswitch I44 en,- gaging the fixed contact II 5, the conductor II8, the fixed contact I2I engaged by the movable contact arm I29 on the relay I20, the conductor I30, the relay 56 and the resistor I45 to ground, thus energizing the relay 56. This causes the movable contact arm 55 to engage the contact 54, thereby connecting the condenser 5I to the cathode I42 of the cathode follower I40. This is the sampling operation and it produces a voltage across the condenser 5I which is proportional to the instantaneous value of the voltage input supplied to the tube I40 from the input lead I3.

The voltage across the condenser 5I is impressed upon the control grid 59 of the cathode follower tube 00, the output at the cathode 63 of which is continuously fed through the conductor 01 and the source of compensating Voltage 60 to the first counter stage 60a (Fig. 4).

If the voltage input to the first stage 68a. is larger than the bias voltage provided by the source 2311, the device 26a becomes conducting, thus energizing the relays 330. (Fig. 4) and 83a (Fig. 5). As stated above, upon energization of the relay 83a, the circuits for operating the punch IOI are broken So that the latter is rendered inoperable to perform a punching operation, regardless of which of the relays83b, 83c, 83d, 83c,

10 83) and 039 may subsequently be energized in the conversion cycle.

A given time determined by the condenser I22, say 2!) milliseconds after energization of the relay 56, the relays H0 and I20 (Fig. 3) are energized. Energization of the latter relay disengages the contacts I27 and I29, thereby deenergizing the relay 56 so that the sampling operation is discontinued. The voltage then existing on the condenser 5I remains sensibly constant during the conversion cycle.

Energizat-ion of the relay I I9 closes its contacts I25 and I23. This connects the conductor I4 to the positive terminal of the source of plate supply voltage through the conductors I24 and 52, thereby energizing both the first timing relay 12a and the relay 4Ia which is associated with the gas discharge device 26a (Fig. 4), and simultaneously applies plate voltage to the gas discharge devices 26a, 26b, 26c, 2601, 26c, 26 and 26g.

If the voltage input to the first stage 680. of the counter is less than the biasing voltage provided by the source 23a, neither of the relays 33a nor 83a will have been energized. Consequently, upon energization of the relay 4Ia, the input to the first stage 68a will be passed over Without change to the input of the second stage 68b.

If the voltage input to the second stage 681) is greater than the bias voltage provided by the source 23b, the gas discharge device 261) will become conducting, thereby energizing the relays 33b and 83b (Fig. 5). Energization of the latter relay prepares a circuit to the terminal I00b of the punch IOI so that when the circuit to the terminal I02 is completed upon operation of the punching relay 16, a hole corresponding to the position of the terminal IIlIIb will be punched in a card. Since the relay 33b is energized, subsequent energization of the relay MI) by timing relay 12a passes on to the input of the third stage the difference between the input to the second stage and the bias voltage provided by the source 23b.

If, on the other hand, the input to the second stage is less than the bias voltage provided by the source 23b, neither of the relays 33b and 831) will be energized so that no hole corresponding to the position of the terminal I00b will be punched by the punch IOI. Further, upon energization of the relay MI) by the timing relay 12a, the input to the second stage will be passed on to the input of the third stage without change.

The input to the first stage 68a is thus passed on successively to the inputs of subsequent stages either unchanged or less the value of the bias voltage provided by any source that is less than the magnitude of the input to that stage. Whenever one of the gas discharge devices 26a, 26b, 26c, 26d, 26e, 26f or 26g has been rendered conducting, a circuit will have been prepared to the corresponding terminal I001), I00c, I00d, I00e, I00j or I009 on the punch IIiI so that corresponding holes will be punched in a card by the latter when the punching operation is initiated.

Energization of the timing relay during the timing sequence results in energization of both the timing relay 12d and the relay I03. Operation of the relay I03 impresses the voltage developed across the condenser I08 on the relay I6. As indicated, the condenser I08 introduces a time delay which prevents the relay 16 from being fully energized until after the final timing relay 12] has been actuated. Upon energization of the relay 12f, its contacts 8Ij and 82 are engaged, thereby connecting conductor 66 to ground and discharging the sampling through the resistor 65.

Shortly thereafter, the relay 16 becomes fully energized, and its movable contact arm H3 engages the contact H4. This connects the terminal I82 of the punch ifii (Fig. 5) to those terminals 100b, 1600, W661, I008, 180) and Hwg for which relays 83b, 83c, 83d, 83c, 83 and 839 have been energized during the conversion cycle so that a punching operation is effected and holes corresponding to the binar number to be recorded are punched in a card.

Operation of the punching relay l6 actuates the Microswitch Hi4 (Fig. 3), moving its contact arm 1'! out of engagement with the contact H5. This breaks the connection between the conductor H8 and the positive terminal of the source of plate supply so that the relays H9 and I2 are deenergized. Deenergization of the relay i 19 disconnects the conductor '54 from the conductor 52. However, electrical energy continues to be supplied temporarily to the timing relays (Fig. 3) and to the plates of the gas discharge devices in the several conversion stages (Fig. through the Microswitch movable contact arm 'i'l which is now in engagement with the contact 15. Deenergization of the relay i2!) prepares a circuit to the sampling relay 56 which is completed when the Microswitch M4 returns to its initial position at the end of the conversion cycle.

After the condenser [68 has been discharged sufliciently, the relay is is deenergized, causing its contacts H3 and H4 to become disengaged. Simultaneously, the Microswitch M4 is released so that its contact arm I? is moved out of engagement with the contact [5 and into engagement with the contact H5. The breaking of the contacts and 'l! removes the plate supply voltage from both the timing relays (Fig. 3) and condenser 5'1 the gas discharge devices in the several counter A stages (Fig. 4). Hence the latter become nonconducting and any energized relays 33a, 33b, 33c, 33d, 33c, 33) and 33g and 83a, 83b, 83c, 83d, 83c, 837' and 839 are restored to the normal deenergized condition. The closing of the contacts T! and H5 again energizes the sampling relay 55, thus initiating a new sampling operation, whereupon the conversion cycle is repeated essentially in the manner described above.

The resistor H52 in shunt with the relay 56 introduces a time lag which is suificient to insure complete deenergization of the last timing relay 12 before the relay T6 is energized, so as to avoid possible loading of the cathode follower 5G by the resistor 65.

If desired, a resistor [53 may be connected in shunt with the last timing relay 12] (Fig. 3) to allow sufficient time for the contacts on the relay Al to close and for the gas discharge device 585 to fire if it is to be fired, before the relay contacts ill) and 82f (Fig. 3) close and discharge the sampling condenser 51.

Actually, the relays 83g, 831, 83c, 83d, B30, 831) and 83a correspond to successive powers of two, the relays 83g and 83a representing the zero and sixth powers, respectively. If, for example, the voltage input to the first counter stage 680 (Fig. 4) is such that the relays 83b and 8303 should be actuated at the end of a conversion cycle, the first gas discharge device 28d will not fire, but the entire input voltage will be passed on to the second stage 681). Here, the voltage input will be greater than the bias voltage supplied by the source 231), so that the gas discharge device 282) will fire. Accordingly, the voltage input to the 12 third stage 680 will be the original input less 50 volts, the bias provided by the source 231). The input to the third stage 680 will not be suflicient to fire the gas discharge device 260 but will be passed on unchanged to the fourth stage 6811. The fourth stage input will be greater than the bias provided by the source 2301 so that the gas discharge device 25d will fire. Hence, the input passed on to the fifth stage will be the fourth stage input less 12.5 volts, the bias provided by the source 23d. In the present case, the diilerence voltage (if any) will not be suflicient to fire any of the gas discharge devices 25c, 25, and 269.

The actual binary number set up in the punch l0! can be observed visually by closing the switch 93. This will light lamps 98a, 96b, 96c, 96d, C52, 56f or 969 corresponding to such of the relays 83a, 83b, 83c, 83d, 83e, 83f and 83g as may be energized at the end of a conversion cycle. Thus, for the case given above, the lamps b and 96d, corresponding to the'digital numbers 32 and 8, respectively, would be lighted.

In the foregoing description, the system is operated self-cycling, namely, the time at which reading and punching occurs is controlled by the system itself. The system is preferably designed so that the self-cycling operation occurs at a frequency determined by the fastest time the punch IOI can punch and skip. For a standard punch of conventional type, a self-cycling speed of one punch every 89 milliseconds is satisfactory and is easily attainable with the present system. However, if more rapid apparatus is available for punching or otherwise recording binary numbers, the self-cycling speed of the digital conversion system can be sensibly increased.

Instead of operating the conversion system self-cycling as described above, the apparatus may be cycled at any desired rate by any suitable control mechanism. This might be accomplished, for example, by short circuiting the leads to the relay I03 and connecting the leads H6 and H1 (Fig. 3) to an intermittently operated switch (not shown). It will be understood that each time the switch is closed, a punching operation will occur and the reader will reset itself for the next punching operation essentially in the manner described above.

As stated, the digital conversion system of the invention can be used to record values of any variable that can be represented by a correspondingly varying electric signal. For example, curves present in the technical literature can be read by a conventional photomultiplier tube or the like, the output voltage of which can be fed to the input lead l3 (Fig. 3) of the digital conversion system. Also, the output of the system maybe read or recorded by other devices than the card punch HH (Fig. 5) which is shown by way of example.

From the foregoing, it will be apparent that the invention provides a novel and highly effective system for converting values of a variable quantity to digital binary numbers in which form they can be recorded directly as perforations in punch cards, for example. By virtue of the novel construciton described above, large quantities of data may be recorded at high speed and in very convenient form for subsequent treatment such as calibration, the application of corrections and other statistical operations, for example. The apparatus is further capable of recording effectively discontinuous values of a variable quantity.

It will be understood that the specific embodiments described above and illustrated in the drawings are susceptible of numerous modifications in form and detail within the scope of the invention. For example, hard tubes in "flip-flop circuits or the like might be used in place of the gas discharge devices 26a, etc. Transistors might also be employed for this purpose. Other modifications will be readily apparent to persons skilled in the art. The particular embodiments disclosed herein, therefore, are not to be regarded as imposing any limitations whatsoever upon the scope of the following claims.

I claim:

1. In an electrical circuit having input terminals and output terminals, the combination of a first channel adapted to be interposed between said input and output terminals, a second channel adapted to be interposed between said input and output terminals and including a source of electrical energy, and electrical means responsive to a function of the signal input to said input terminals and of the voltage of said source, for selectively controlling the interposition of said first and second channels between said input and output terminals.

2. In an electrical circuit having input terminals and output terminals, the combination of circuit means connected to one of said input terminals and having a source of voltage connected in series therewith, switching means for selectively connecting one of said output terminals to said one input terminal or to said circuit means, and relay means responsive to a function of both the input to said input terminals and the voltage of said source for controllin the operation of said switching means.

3. In an electrical circuit having input terminals and output terminals, the combination of circuit means connected to one of said input terminals and having a source of voltage connected in series therewith, switching means for selectively connecting one of said output terminals to said one input terminal or to said circuit means, an electron tube having a grid connected to said circuit means and having plate and cathode electrodes, and relay means connected in the platecathode circuit of said tube for controlling the operation of said switching means.

4. In an electrical circuit having input and output terminals, the combination of an electron tube having plate, grid and cathode electrodes, circuit means including a source of bias voltage interposed between one of said input terminals and the grid of said tube, switching means normally connecting one of said output terminals to said one input terminal and adapted to connect said one output terminal to the terminal of said bias voltage nearest said grid, and relay means interposed in the plate-cathode circuit of said tube for actuating said switching means to disconnect said one output terminal from said one input terminal and to connect said one output terminal to said bias voltage terminal.

' 5. In an electric circuit having input and output terminals, the combination of circuit means connected to one of said input terminals, first switching means having a pair of fixed contacts connected to said circuit means and to said one input terminal, respectively, and having a movable contact adapted to engage either of said fixed contacts selectively, second switching means having a pair of fixed contacts connected to the movable contact of said first switching means and to said circuit means, respectively, and having a movable contact connected to one of said output terminals and adapted to engage either of said fixed contacts, first relay means for actuating said first switching means and second relay means responsive to a 'function of the input to said input terminals for actuating said second switching means.

6. In an electrical circuit having input and output terminals, the combination of circuit means connected to one of said input terminals, first switching means having a first contact connected to said circuit means, a second contact connected to said one input terminal and a movable contact normally engaging said first contact but adapted to be moved into engagement with said second contact, second switching means having a first contact connected to themovable contact on said first switching means, a second contact connected to said circuit means, and a movable contact connected to one of said output terminals, said movable contact normally engaging the first contact of said second switch,- ing means but being adapted to be moved into engagement with the second contact thereof, first relay means for actuating said first switching means, and second relay means responsive to a function of the input to said input terminals for actuating said second switching means.

7. In an electrical circuit having input and output terminals, the combination of an electron tube having plate, grid and cathode electrodes, circuit means including a'source of bias voltage interposed between one of said input terminals and a grid of said tube, firstswitching means having a first contact connected to the terminal of said bias voltage nearest said grid, a second contact connected to said one input terminal, and a movable contact normally engaging said first contact but being adapted to be moved into engagement with said second contact, second switching means having a first contact connected to the movable contact of said first switching means, a second contact connected to said bias voltage terminal, and a movable contact connected to one of said output terminals and normally engaging the first contact of said switching means but being adapted to be moved into engagement with the second contact thereof, first relay means for actuating said first switching means, and sec ond relay means connected in the plate-cathode circuit of said tube for actuating said second switching means.

8. In apparatus for converting values of a,variable to digital numbers, the combination of circuit means having an input terminal and including a source of voltage representing a digital number, an output terminal, first switching ,means responsive to a function of the input supable to digital numbers, the combination of a plurality of stages each comprising circuit means having an input terminal and including a source of voltage representing a digital numher, the voltages in successive stages being different and corresponding to different digital numbers, respectively, first switching means each stage and responsive to a function of both 15 the input to that stage and of the "voltage provided by the source therein for connecting the input terminal of the circuit means in the next succeeding stage selectively to the circuit means vof the preceding stage or to another terminal therein, second switching means in each stage for connecting said another terminal selectively :to the circuit means of that stage or to the input terminal thereof, mechanism for actuating the second switching means in each of .said

stages :in succession, and means for each of said stages rendered operative when said function of the input to each stage and of the voltage the circuit means in the next succeeding stage selectively to the circuit means of the preceding stage or to another terminal therein, second switching means in each stage for connecting said another terminal in that stage selectively to the circuit means therein or to the input terminal thereof, first relay means in each stage and connected in the plate-cathode circuit of the gas discharge device therein for actuating the first switching means thereof, .second relay means in each stage for actuating the second switching means thereof, timing mechanism for successively energizing the second relay means in each of said stages, and a plurality of relays connected in the plate-cathode cirsuits of said gas discharge devices, respectively.

11. In apparatus for converting values of a variable to digital numbers, the combination of a plurality of stages each comprising a. .gas discharge device having plate, grid and cathode electrodes, .and circuit means including a, source of bias voltage connected at its opposite ends to :an input terminal and to .a grid of said device, respectively, the bias voltages in successive stages being different and corresponding to different digital numbers, first switching means in each stage for connecting the input terminal of the circuit means in the next succeeding stage selectively to the circuit means of the preceding stage or to another terminal therein, second switching means in each stage for connecting said another terminal in that stage selectively to the circuit means therein or to'the input terminal thereof, first relay means in each stage and connected in the plate-cathode circuit of the gas discharge device therein for actuating the first switching means thereof, second relay means in each stage for actuating the second switching means thereof, electrical means responsive to electrical values corresponding to values of a variable for impressing an electric signal representative of the instantaneous value of said variable upon the input terminal of the circuit means in "the first of said stages, timing mechanism initiated in timed relation to the production of said signal for successively eneragizing the second relay means in each of said stages, and a plurality of :circuit preparing re- 16 lays connected in the plate-cathode circuits of said gas discharge devices, respectively.

'12. In apparatus for converting values of a variable to digital numbers, the combination of .a plurality of stages each comprising a gas discharge device having plate, grid and cathode electrodes, and circuit means including a source of bias voltage connected at its opposite ends to an input terminal and to a grid of said device, respectively, the bias voltages in successive stages differing by a factor of two and corresponding to diiferent binary digital numbers, first switching means in each stage for connecting the input terminal of the circuit means in the next succeeding stage selectively to the circuit means of the preceding stage or to another terminal therein, second switching means in each stage for connecting said another terminal in thatstageselectively to the circuit means therein or to the input terminal thereof, first relay means ineach stage and connected in the plate-cathode circuit of the gas discharge device therein oi-actuating the first switching means thereof, second relay means in each stage for actuating the second switching means thereof, electrical sampling means responsive to electrical values correspond- :ing to values-of a variable for delivering a signal representative of the instantaneous value of said variable periodically to the input terminal of the circuit means in the first'of said stages, timing mechanism initiated in tizned relation to the delivery of signals for successively energizing the second relay means in each of said stages,

and a plurality of circuit preparing relays :connested in the plate-cathode circuits of said gas discharge devices.

13. in digital conversion apparatus as defined in claim 12, the combination of a plurality of switching means adapted to be actuated by said circuit preparing relays, respectively, a binary code card perforating punch for recording the output of said plurality of switching means, said punch having a plurality of circuits connected to said last-named switching means, respectively, and adapted to be prepared by operation-thereof, and relay means rendered operatr-e by said timing ;mechanism for enabling such of said lastnamed circuits as have been prepared and for operating said punch.

14. In digital conversion apparatus as defined in claim 10, the combination of a plurality of indicating means, and a plurality of switching means adapted to be actuated by the relays in the plate-cathode circuits of said gas discharge devices, respectively, for operating said respective indicating means.

15. In digital conversion apparatus as defined in claim 12, the combination of a plurality of switching means adapted to be actuated by said circuit preparing relays, respectively, a card perforating punch having a plurality of circuits connected to said last-named switching'means, re-

named'relayzmeans again becomes inoperative for delivering a new signal value to the input terminalof the circuit means in the firstnfsaidstages. :16. In digital conversion apparatus as defined in claim 10, the combination of electrical sampling means including a condenser adapted to be charged periodically to electrical values corresponding to values of a variable for delivering signals respectively representative of instantaneous values of said variable periodically to the input terminal of the circuit means in the first of said stages, a plurality of switching means adapted to be actuated by the relays in the platecathode circuits of said gas discharge devices, respectively, a card perforating punch having a plurality of circuits connected to said last-named switching means, respectively, and adapted to be prepared by operation thereof, relay means rendered temporarily operative by said timing mechanism for completing such of said last-named circuits as have been prepared and for operating said punch, means operated by said timing mechanism for discharging said condenser to erase the signal value delivered to the input terminal of the circuit means in the first of said stages, and means rendered operative when said last-named relay means again becomes inoperative for charging said condenser to an electrical value corresponding to a new value of said variable, thereby delivering a new signal to the input terminal of the circuit means in the first of said stages.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,371,040 Fisher et a1 Mar. 6, 1945 2,401,621 Desch et a1. June 4, 1946 2,436,512 Hollywood Feb. 24, 1948 2,422,428 Mumma June 1, 1948 2,451,859 Mumma et a1 Oct. 19, 1948 2,457,214 Doll et a1. Dec. 28, 1948 2,466,467 Mumma et al Apr. 5, 1949 2,495,075 Mumma Jan. 17, 1950 2,513,112 Shepherd June 27, 1950 2,536,955 Palmer Jan. 2, 1951 

